1. Field of the Invention
The present invention relates to a detection apparatus, and more particularly to a contactless detection apparatus and method for detecting a rotation direction.
2. Description of Related Art
In response to the concept of the environmental awareness and the exercise regimen, more and more people take a bike as a daily exercising device or a daily commuting tool. However, the riding distance and the terrain are not proper for everyone. Not everyone has enough physical strength to sustain through the riding action. As a result, an electric bike is manufactured to assist the exerciser with riding a bike.
A conventional electric bike has a throttle switch and a motor installed on a bike. The motor is used to provide a pushing force to move the bike ahead. When the exerciser wants to activate the motor, the exerciser has to manually turn on the throttle switch. However, when the exerciser is riding, the exerciser needs to pay attention on the road ahead and operates the throttle switch at the same time. The complication for riding the electric bike is high.
In addition, the pushing force is not provided immediately. The motor does not provide the pushing force until the exerciser steps on a crank of the bike over a half of a circular spinning movement. As a result, the exerciser still uses great effort to ride on the bike as before. The conventional throttle switch and the motor do not efficiently assist the exerciser with riding the bike.
Responsive to such problems, a conventional detection device is used to detect a twisting torque and a twist angle of a shaft of a bike. The motor can be automatically activated to offer the pushing force according to the detected twisting torque and the twist angle.
With reference to FIGS. 17A and 17B, a first conventional detection device is disclosed. The detection device is adapted to be mounted on an input shaft 81 and an output shaft 82, wherein the input shaft 81 is connected to the output shaft 82 through a coupler 83. The detection device has a first magnet array 811, a second magnet array 821 and a magnetic sensor 84.
The coupler 83 and the magnetic sensor 84 are mounted between the input shaft 81 and the output shaft 82. The first magnet array 811 is mounted around the input shaft 81. The second magnet array 821 is mounted around the output shaft 82. Each magnet array 811, 821 respectively has multiple north poles (N) and south poles (S) arranged alternately. A number of the poles (N, S) of the first magnet array 811 is equal to a number of the poles (N, S) of the second magnet array 821. The north poles (N) and the south poles (S) of the first magnet array 811 are respectively aligned with the north poles (N) and the south poles (S) of the second magnet array 821.
When the input shaft 81 rotates, the input shaft 81 turns the output shaft 82 through the coupler 83. The coupler 83 is designed to flex when a torque is applied to either shaft, resulting in an angular displacement between the input shaft 81 and output shaft 82. The north poles (N) of the first magnet array 811 are not exactly aligned with the north poles (N) of the second magnet array 821, neither are the south poles (S) of the first magnet array 811 and the second magnet array 821. As a result, the magnetic field between the first magnet array 811 and the second magnet array 821 is changed. The magnetic sensor 84 can detect the changed magnetic field. According to the changed magnetic field, a twisting torque exerted on the input shaft 81 and the output shaft 82 can be calculated.
With reference to FIG. 18, to detect a rotational angle of a shaft 85, a first magnet array 851 and a second magnet array 852 are mounted around the shaft 85 and are adjacent to each other, wherein a sensor 86 is mounted between the magnet arrays 851, 852. The first magnet array 851 and the second magnet array 852 respectively have different number of poles (N, S). The first magnet array 851 has N pairs of poles (N, S) and the second magnet array 852 has N+1 pairs of poles (N, S). In an initial condition, the poles (N, S) of the first magnet array 851 are not actually aligned with the poles (N, S) of the second magnet array 852. When the shaft 85 rotates, the poles (N, S) of the first magnet array 851 tend to align with the opposite poles (N, S) of the second magnet array 852. As a result, the magnetic sensor 86 can detect the change of the magnetic field between the first magnet array 851 and the second magnet array 852. According to the changed magnetic field, the rotational angle of the shaft 85 can be calculated.
With reference to FIG. 19, however, the first conventional detection device needs at least three magnet arrays 811, 821, 852 to achieve the detecting action. Each magnet array 811, 821, 852 is composed of many pairs of poles (N, S). The first conventional detection device is not easy to be manufactured and causes high cost. Moreover, the magnetic fields between the three magnet arrays 811, 821, 852 may interfere with each other, such that the detection result of the first conventional detection device is not accurate.
With reference to FIG. 20, a second conventional detection device is disclosed. A top tube 91 and a bottom tube 92 are respectively mounted on a shaft. The top tube 91 and the bottom tube 92 respectively have a disk 911, 921. The disks 911, 921 have equal number of poles (N, S). The second conventional detection device has two Hall sensors 931, 932 respectively mounted beside the poles (N, S) of the two disks 911, 921. The Hall sensors 931, 932 detect the magnetic fields of the poles (N, S) of the disks 911, 921. According to the detected magnetic fields, a twisting torque exerted on the shaft can be calculated.
However, such detection device is only able to detect the twisting torque. A twist angle of the shaft cannot be detected at the same time. Hence, the function of the detection device is limited.